projecting microscope would be a good way to do. Niko.

if it’s connected with your seat motor wasn’t a Metric 2.5mm component mentioned – from diameter this sounds rather like a M2.5 thread wch should be 0.45mm (a M2.5 fine is 0.35 thread – a M2 would have 0.4 but not that diameter

Is it an old or new dial gauge as this would give some idea of what the thread may be, a new far eastern import is probably metric M2.5. An old English one probably 7BA or 8BA, Amereican will be UNC or UNF.

Is there any plain shanlk beyond the thread as that could also give a clue as it will eliminate any overcutting of the thread.

Edited By JasonB on 11/06/2016 07:34:38

YOu have the perfect instrument to mesure the pitch right there. Set the plunger shaft tip on a flat surface, with dial gauge suitably bolted down. Set dial to zero. Mark the shaft. Rotate shaft tip one turn so that the thread unscrews. Read the pitch off the dial gauge dial.

I am also trying to do the same as you, but for a different reason, making an adaptor to set timing on a two stroke motor cycle engine.

I am getting same sort of readings as you i.e. 2.42 mm major thread diameter.

I have poor eye sight and not able to compare thread with a thread pitch gauge, even with the aid of an illuminated magnifier.

I have 7BA and 2.5mmx.45 taps and these do not fit the thread in the DTI shaft.

Edited By Chris Shelton on 11/06/2016 17:11:38

UNF fine #2 2.1844mm nom dia 0.3969mm (64tpi) thread – nom dia + half thread = pretty much what you have – made for North American market ?

Harold Halls book is cheap and has many useful tables saves hitting the Net when you have a workshop query (if only it could be printed on oil proof (or wipe clean) paper
also guess 1/64th inch very convenient measure!

Edited By Frances IoM on 11/06/2016 17:48:10

Edited By Frances IoM on 11/06/2016 17:51:23

I do not see the problem, why do you want to know the pitch with 3 digits behind the decimal for such a short thread, be practical, M 2.3 has a pitch 0.4 mm. Make the type you want and if it fits it fits. I have done the same for the one I have. Niko.

Niko – guess as being used in a precise instrument needs a very firm fit between the gauge and the extension rod and guess doesn’t want to damage the original thread

CFE. College of Further Education. The place where many went to learn a bit more after leaving school. I worked there. Uni's (where you might get a full time degree) are another option. Many of us with a science degree have used these instruments for a range of scientific experiments.

I often scale things from digital photos. Prop the part up with some Blu Tack and put a steel rule close to it at the same height as the centreline (so as to place both in the same plane. Take the best image you can (with a macro focus option if available), and scale it up to fill your monitor. Then measure on the screen the screw pitch and the steel rule – use a plastic ruler to avoid scratching the screen. Apply the scale ratio from the photo to the component, i.e.

Pitch = real inches x photo pitch / photo inches

or

Pitch = real mm x photo pitch / photo mm

You can do the same thing (upside down) using a scanner, I used to do this to check plastic extrusions in the absence of a shadowgraph.

Brian

deja vu